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Frequency estimation of undersampled waveforms receives increasing attention in communication, radar signal processing, instrumentation and measurements, and so on. However, due to the lack of recognizing the correct remainder between two side spectra, the existing Chinese Remainder Theorem (CRT)-based frequency estimators can hardly deal with real-valued signals. To achieve this goal, this paper proposes an estimator combining spectrum correction (aiming to enhance reconstruction accuracy by incorporating the fractional parts of DFT remainders), closed-form CRT, and a remainder sifting approach. Based on the detection of an undersampled waveform's zero crossing point, this solution can pick out the correct remainder between two side spectra, which ensures that the CRT achieves a valid reconstruction. Compared with the existing Maroosi-Bizaki estimator, the proposed method not only enlarges the upper bound of frequency recovery but also possesses higher reconstruction accuracy (the relative error is less than 0.002%) with lower consumption of computational complexity. The numerical results verify the superior performances of our estimator.

Multiuser transmission with shared spectrum is investigated in the presence of energy harvesting. For each user, the data generation, the harvested energy arrival, and the channel state variation are, respectively, considered as stochastic processes. Each user aims to maximize its own average throughput. Accordingly, a stochastic game is formulated at first. Next, we analyze the stochastic game in infinite-stage and finite-stage scenarios, respectively. On the basis of theoretical studies, an iterated distributive algorithm with solving a linear problem in each iteration is designed for the infinite case. For the finite case, two distributed algorithms named CVPBI and GoPGA are proposed. Finally, the effectiveness of the proposed algorithms is demonstrated by simulations.

Sintered rare-earth permanent magnets (for example, Sm2 Co17, SmCo5, and Nd2 Fe14B magnets) are quite brittle and easily crack in the course of fabrication, machining, and application. Here, we report on an investigation of fracture behavior and mechanical characteristics of sintered rare-earth permanent magnets and discuss the origin of rare-earth magnet brittleness. We studied three groups of bending specimens with different orientations, cut from the same block of magnet The bending strength was measured. The fracture surfaces were carefully observed by scanning electron microscopy and showed that the fracture behavior and bending strength of Sintered rare-earth permanent magnets obviously exhibit anisotropy. Sintered Sm-Co magnets tend to cleavage fracture in the close-packed (0001) plane or in the (1011) plane. The fracture mechanism of sintered Nd2 Fe14 B magnet appears to be mainly intergranular fracture. Our analysis indicates that the anisotropy of fracture behavior and mechanical strength of sintered rare-earth magnets is caused by the strong crystal-structure anisotropy and grain texture created by magnetic field alignment during the fabrication process. [ABSTRACT FROM AUTHOR]

Sintered Sm2 Co17 magnets are widely used in aviation, spaceflight and precision instruments, etc. Thermal expansion coefficients a are necessary engineering data for the precision applications of the magnets (α presents the average thermal expansion coefficient). Here, we report an investigation on thermal expansion of sintered Sm2CO17 magnets. The effects of the substitutions of Gd, Dy, Er, and Pr for Sm on thermal expansion characteristics were discussed, respectively. The thermal expansion characteristics were measured using a NETZSCH DIL 402C thermal dilatometer. α// is the thermal expansion coefficient in the c axis and α⊥ is the coefficient in the base plane. All the specimens for each material were cut from the same block. A scanning electronic microscope (SEM) equipped with an energy dispersive x-ray analysis system is employed to observe the microstructure. It shows that the thermal expansion coefficient of Sm2Co17 magnets obviously exhibit anisotropy. The α⊥ is higher than the α//. The thermal expansion coefficient (both α⊥ and α//) increases and the thermal expansion anisotropy (α⊥ - α//) decreases with increasing temperature. The substitutions of heavy-rare earth elements, such as Gd+Dy, and Er decrease α//, the substitution of Pr for Sm moderately increases α//. The phenomenon is especially obvious in low-temperature range. [ABSTRACT FROM AUTHOR]